1. Field of the Invention
The present invention relates to an electric-component transferring apparatus, a method of taking respective images of electric components (i.e., circuit components as elements of an electric or electronic circuit), and a system for mounting electric components on a circuit substrate such as a printed circuit board.
2. Related Art Statement
There is known an electric-component (xe2x80x9cECxe2x80x9d) transferring device which includes an EC holder for holding an EC, a shaft member for supporting the EC holder, and a moving device for moving the EC holder in a direction intersecting an axis line of the shaft member, and thereby transferring the EC in that direction. This sort of EC transferring device is disclosed in, e.g., Japanese Patent Application laid open for public inspection under No. 8(1996)-78882. The disclosed device includes an EC holder which holds an EC; a shaft member whose lower end portion supports the EC holder; a movable member having a support hole which supports the shaft member such that the shaft member is rotatable about an axis line relative to the movable member and is movable relative to the movable member in an axial direction parallel to the axis line; and a moving device which moves the movable member in a direction intersecting the axis line of the shaft member.
The above-indicated EC transferring device is employed as an EC mounting device which takes an EC from an EC supplying device and mounts the EC on a printed circuit board (xe2x80x9cPCBxe2x80x9d) as a sort of circuit substrate that is an object on which ECs are to be mounted. The EC mounting device includes an EC mounting head; an X-Y robot which moves the EC mounting head in each of two directions perpendicular to each other on a horizontal plane; a Z-axis/xcex8-axis motor which is provided on the X-Y robot, which moves the head in a vertical direction (i.e., a Z-axis direction) perpendicular to the horizontal plane, and which rotates the head about a vertical axis line; and an EC-image taking device which is provided between the EC supplying device and the PCB.
The Z-axis/xcex8-axis motor includes a Z-axis motor portion and a xcex8-axis motor portion which are integrated with each other and each of which includes an AC servomotor (i.e., brushless DC servomotor). The Z-axis motor portion further includes a nut which is supported by an upper portion of a housing such that the nut is rotatable about a vertical axis line and is not movable in an axial direction parallel to the axis line; and a ball screw which is fitted in the housing such that the ball screw is movable in an axial direction thereof, and is not rotatable, relative to the housing and which is screwed with the nut. A permanent magnet which is fixed to an outer circumferential surface of the nut provides a rotor of the AC servomotor of the Z-axis motor portion. The rotor is opposed to a stator core which is provided in the housing. The stator core includes a plurality of coils. An electric current which is supplied to the coils is so controlled as to rotate the nut by an arbitrary angle in each of opposite directions and thereby move the ball screw over an arbitrary distance in each of upward and downward directions.
A lower portion of the housing supports a ball-spline member which is concentric with the ball screw and which is rotatable, and is not movable in an axial direction thereof, relative to the housing. A spline-axis member is fitted in the ball-spline member such that the spline-axis member is not rotatable, and is movable in an axial direction thereof, relative to the ball-spline member. A permanent magnet which is fixed to the ball-spline member provides a rotor of the AC servomotor of the xcex8-axis motor portion. The rotor is opposed to another stator core which is provided in the housing. The second stator core includes a plurality of second coils. An electric current which is supplied to the second coils is so controlled as to rotate the ball-spline member by an arbitrary angle in each of opposite directions and thereby move the spline-axis member over an arbitrary angle in a corresponding one of the opposite directions.
The spline-axis member is connected to the ball screw such that the spline-axis member is rotatable, and not movable in its axial direction, relative to the ball screw. The EC mounting head is attached to a lower end portion of the spline-axis member. The spline-axis member and the ball screw cooperate with each other to provide a shaft member whose lower end portion supports an EC holder, and respective inner holes of the nut and the ball-spline member cooperate with each other to define a support hole which supports the shaft member. When the ball screw is moved up and down, the spline-axis member is moved up and down and the EC mounting head is moved up and down. When the spline-axis member is rotated, the head is rotated about its axis line. While the head is moved down and then up, the head takes an EC from the EC supplying device, or mounts the EC on the PCB. While the head is rotated, a possible angular error of the EC held by the head from a reference angular position about a vertical axis line may be corrected. Since the EC mounting head is moved up and down, and rotated, by the single Z-axis/xcex8-axis motor including the upper Z-axis motor portion and the lower xcex8-axis motor portion integrated with each other, the EC mounting device enjoys a simple construction as compared with one in which a Z-axis motor and a xcex8-axis motor are employed as separate members.
However, the two servomotors are used, one for moving the EC mounting head up and down, and the other for rotating the head. In addition, the ball screw and the spline-axis member are connected to each other such that they are rotatable, and not movable in their axial direction, relative to each other. Thus, the EC mounting device suffers from a high production cost. Moreover, since the nut, the ball-spline member, the rotors, and the stators are provided around the ball screw and the spline-axis member, the EC mounting device suffers from a large size.
Japanese Patent Application laid open for public inspection under Publication No. 7(1995)-45995 discloses an EC mounting system including an EC sucker which sucks and holds an EC by applying vacuum thereto, and an EC supplying device which supplies an EC to the EC sucker. Thus, the EC sucker takes the EC from the EC supplying device, and subsequently mounts the EC on a CS. However, the EC held by the EC sucker may have an positional error from a reference position on a plane intersecting an axis line of the EC sucker. This positional error is an error of the center of the EC relative to the axis line of the EC sucker, and results from the dislocation of the EC on the EC supplying device, from its reference position relative to the supplying device, and/or the misalignment of the EC relative to the EC sucker when the EC is sucked by the sucker. To solve this problem, it has been practiced to employ an EC-image taking device which takes an image of the EC taken by the EC sucker from the EC supplying device and calculate, based on the taken image, a positional error of the EC held by the sucker from its reference position relative to the sucker. This positional error is corrected before the EC is mounted on the CS, and accordingly the EC is accurately mounted at a prescribed EC-mount place on the CS.
In the above-indicated EC mounting system, the EC sucker is supported by a movable member which is movable in each of an X-axis and a Y-axis direction which are perpendicular to each other on a horizontal plane, and the EC-image taking device is provided between the EC supplying device and a CS supporting device which supports the CS. While the EC sucker is moved toward the CS supporting device after taking the EC from the EC supplying device, the EC-image taking device takes an image of the EC held by the EC sucker.
In the above EC mounting system, the movable member supports the single EC sucker. Therefore, each time one EC is mounted on the CS, the movable member goes and backs between the EC supplying device and the CS supporting device. If the movable member would support a plurality of EC suckers, a plurality of ECs could be mounted on the CS while the movable member goes and backs one time between the EC supplying device and the CS supporting device. This would lead to improving the efficiency of mounting of ECs.
However, the EC-image taking device can take, at one time, an image of only one EC. Therefore, each time an image of one EC is taken, the movable member must be moved to position the next EC at an image-take position. This operation needs a long time, which leads to lowering the efficiency of mounting of ECs.
It is therefore an object of the present invention to provide an electric-component transferring apparatus which moves a component holder holding an electric component, in an axial direction thereof, and rotates the holder about an axis line thereof and which enjoys a low cost and a compact construction.
It is another object of the present invention to provide an electric-component mounting system including the above electric-component transferring apparatus.
It is another object of the present invention to provide a method of taking respective images of electric components with high efficiency.
It is another object of the present invention to provide an electric-component mounting system for mounting electric components with high efficiency.
The present invention provides an electric-component transferring apparatus, an electric-component mounting system, and an electric-component-image taking method which have one or more of the technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (31). Any technical feature which includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to that technical feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the scope of the present invention is by no means limited.
(1) According to a first feature of the present invention, there is provided an electric-component transferring apparatus comprising at least one component holder which holds an electric component; at least one shaft member whose lower end portion supports the component holder; a movable member having at least one support hole which supports the shaft member such that the shaft member is rotatable about an axis line relative to the movable member and is movable relative to the movable member in an axial direction parallel to the axis line; a moving device which moves the movable member in a direction intersecting the axis line of the shaft member; a piston which is supported by the shaft member such that the piston is not movable relative to the shaft member in the axial direction of the shaft member; the support hole including a portion defining a cylinder bore which cooperates with the piston to provide an air-pressure-operated cylinder device; a driven wheel which is substantially integral with the shaft member; a drive wheel which is supported by the movable member such that the drive wheel is meshed with the driven wheel to rotate the driven wheel; and one of the drive wheel and the driven wheel having a length which assures that the drive and driven wheels are kept meshed with each other when the driven wheel is moved with the shaft member in the axial direction thereof. It is preferred that the movable member be one which is moved by the moving device in a direction perpendicular to the axis line of the shaft member, for example, one which is moved in each of two directions which are parallel to an X axis and a Y axis, respectively, which are perpendicular to each other on a horizontal plane, or one which is rotated about a vertical axis line. On the movable member, the shaft member may be moved in its axial direction not only by the air-pressure-operated cylinder device (hereinafter, referred to as the xe2x80x9cair cylinderxe2x80x9d) but also by another device independent of the air cylinder. The component holder may be one, in accordance with a second feature (2) described below, which includes a suction nozzle which sucks and holds an electric component (xe2x80x9cECxe2x80x9d) by applying vacuum thereto; one which includes a grasping device which includes a plurality of grasping members and grasps and releases an EC by closing and opening the grasping members; or any one of various known holders. The component holder may be one which is produced integrally with the shaft member; or one which is produced as a member which is separate from the shaft member and which is detachably attached to the shaft member. The axial line of the shaft member may not be vertical, that is, the shaft member may extend in a direction inclined with respect to a vertical direction. The air cylinder may be of a single-action or double-action type. The present EC transferring apparatus transfers an EC by moving the movable member and accordingly the shaft member, thereby moving the component holder to a position above the EC, and operating the air cylinder to lower the shaft member so that the component holder holds the EC. Subsequently, the air cylinder is operated to elevate the shaft member so that the component holder picks up the EC, and the movable member is moved to move the shaft member and thereby transfer the EC so that the EC is received by an EC receiving member such as a PCB. In the case where an angular error of the EC held by the component holder from a reference angular or rotation position is corrected and/or a current angular position of the EC at which the EC is picked up by the holder is changed to a prescribed angular position at which the EC is received by the EC receiving member, the driven wheel is rotated by the drive wheel, so that the shaft member and the component holder are rotated about their axis line and accordingly the EC is rotated. Since one of the drive wheel and the driven wheel has a length which assures that the drive and driven wheels are kept meshed with each other when the driven wheel is moved with the shaft member in the axial direction thereof, the shaft member can be moved in its axial direction while being kept in the state in which the shaft member can receive the rotation of the drive wheel. Since the air cylinder, the driven wheel, and the drive wheel are cheap, the EC transferring apparatus which rotates the shaft member and moves the same in its axial direction enjoys a low production cost. A dimension of the EC transferring apparatus in a direction parallel to the axis line of the shaft member is greater than that of an EC transferring device in which no air cylinder is employed, but is smaller than that of a conventional EC transferring device in which a Z-axis motor and a xcex8-axis motor are provided in series in a direction parallel to an axis line of a shaft member. Thus, the present EC transferring apparatus enjoys a compact construction. Since the drive wheel is provided in series with the shaft member, the dimension of the EC transferring apparatus in the direction parallel to the axis line of the shaft member is increased as such. However, since the drive and driven wheels are just required to transmit rotation to the shaft member, the respective diameters of the wheels can be minimized. Thus, a dimension of the EC transferring apparatus in a direction perpendicular to the axis line of the shaft member is not increased, and the apparatus enjoys a compact construction.
(2) According to a second feature of the present invention that includes the first feature (1), the component holder comprises a suction nozzle which has a vacuum-supply hole opening at a lower end thereof, and which sucks and holds the electric component by applying vacuum thereto. Since the suction nozzle utilizes vacuum for holding an EC, the EC is not damaged.
(3) According to a third feature of the present invention that includes the second feature (2), the suction nozzle is supported by the lower end portion of the shaft member such that the nozzle is slideable relative to the shaft member in the axial direction thereof, and the component holder further comprises a spring member which is provided between the shaft member and the suction nozzle and which biases the nozzle so that the nozzle projects downward from the lower end portion of the shaft member. The spring member may be a tension coil spring or a compression coil spring. In the present EC transferring apparatus, the elastic deformation of the spring member permits the relative movement of the suction nozzle and the shaft member. The stroke of movement of the shaft member by the air cylinder may be determined to be greater than the distance between a lower end of the suction nozzle supported by the shaft member being positioned at its upper stroke-end position, and an upper surface of each EC. In this case, even when the present apparatus transfers different sorts of ECs having different thickness values, or even if there arises a difference between respective height values of different ECs supplied from different EC supplying devices because of the manufacturing errors of the EC supplying devices, the suction nozzle can reliably contact each EC and suck and hold the EC without damaging it. After the nozzle contacts the EC, the shaft member is further moved downward over a small distance. This downward movement is allowed by the elastic deformation of the spring member. Thus, the difference between the thickness or height values of the ECs is well accommodated.
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the piston is supported by an upper end portion of the shaft member. Since the piston is supported by the upper end portion of the shaft member, the air cylinder can be easily constructed. The piston may be supported by an intermediate portion, or a lower end portion, of the shaft member. In the latter case, however, it is difficult to form the cylinder bore and/or define one or both ends of the stoke of movement of the shaft member. In contrast, in the former case where the piston is supported by the upper end portion of the shaft member, a sleeve may be fitted in a portion of a through-hole formed in the movable member, so that a portion of the support hole is provided by an inner hole of the sleeve, and the cylinder bore may be defined by the remaining portion of the through-hole. In the last case, the sleeve defines the lower end of the stroke of the shaft member. In this way, the air cylinder is easily constructed.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the piston is produced separately from the shaft member and then is attached to the shaft member.
(6) According to a sixth feature of the present invention that includes any one of the first to fifth features (1) to (5), the piston is not rotatable relative to the shaft member. The piston may be completely fixed to the shaft member, if the piston can be rotated in the cylinder bore when the shaft member is rotated. In this case, the air cylinder enjoys a simple construction. However, the piston may be substantially airtightly attached to the shaft member such that the piston is rotatable relative to the shaft member.
(7) According to a seventh feature of the present invention that includes any one of the first to sixth features (1) to (6), the piston is provided with no sealing member, and is substantially airtightly fitted in the cylinder bore such that substantially no clearance is left between an outer circumferential surface of the piston and an inner circumferential surface of the bore. In this case, without any sealing members, the piston is substantially airtightly fitted in the cylinder bore. Thus, the total number of parts needed to produce the present apparatus is reduced as such. The sealing members would be worn if they would be used with the piston which is rotated with the shaft member and is moved in its axial direction with the same. The present apparatus is free from this problem.
(8) According to an eighth feature of the present invention that includes any one of the first to seventh features (1) to (7), the EC transferring apparatus further comprises a stopper which is supported by the movable member such that the stopper is opposed to an upper end portion of the shaft member, and which defines an upper stroke end of the movement of the shaft member relative to the movable member, one of the stopper and the shaft member including a projection which is buttable against the other of the stopper and the shaft member at a point on the axis line of the shaft member. The projection contacts the other of the stopper and the shaft member, at a single point defined by the tip of the projection. Therefore, when the shaft member is rotated in the state in which the projection is held in contact with the other of the stopper and the shaft member, the shaft member is subjected to a small resistance only. Thus, the shaft member is smoothly rotated. In addition, the wearing of the shaft member and the stopper is minimized.
(9) According to a ninth feature of the present invention that includes any one of the first to eighth features (1) to (8), the EC transferring apparatus further comprises a stopper which is supported by the movable member such that the stopper is opposed to an upper end portion of the shaft member, and which defines an upper stroke end of the movement of the shaft member relative to the movable member, the stopper including a displaceable member which is displaceable relative to the movable member in a direction parallel to the axis line of the shaft member, and a cushion member which is provided between the movable member and the displaceable member. After the shaft member contacts the displaceable member, the shaft member is further moved to displace the displaceable member while compressing the cushion member, and then is stopped. The impact produced when the shaft member butts against the stopper is absorbed by the cushion member, so that the EC is prevented from falling off the shaft member or being dislocated relative to the same. Since the shaft member butts against the cushion member via the displaceable member, the area at which the shaft member contacts the displaceable member can be minimized. For example, in the case where the shaft member includes a projection and the projection directly butts against the cushion member provided by a rubber member, the projection contacts the rubber member via an area enlarged by the elastic deformation of the rubber member. Thus, the shaft member cannot be smoothly rotated. In contrast, since the shaft member butts against the cushion member via the displaceable member, the shaft member can contact the displaceable member via a single point, which assures that the shaft member is smoothly rotated. In addition, the impact produced when the shaft member is stopped is absorbed by the cushion member.
(10) According to a tenth feature of the present invention that includes the ninth feature (9), the cushion member is formed of a vibration damping rubber which absorbs impact of the displaceable member and damps vibration of the displaceable member. In this case, the impact produced when the shaft member is stopped and the vibration produced after the shaft member is stopped are largely reduced, and the EC is prevented from falling off the component holder or being dislocated relative to the holder because of the impact or vibration.
(11) According to an eleventh feature of the present invention that includes any one of the first to tenth features (1) to (10), the movable member comprises a main member having a sleeve-support hole, and a hollow sleeve fitted in the sleeve-support hole, an inner hole of the hollow sleeve defining at least a portion of the support hole of the movable member.
(12) According to a twelfth feature of the present invention that includes the eleventh feature (11), the sleeve is fitted in a lower portion of the sleeve-support hole of the main member, the cylinder bore including an upper portion of the sleeve-support hole.
(13) According to a thirteenth feature of the present invention that includes the twelfth feature (12), the sleeve-support hole of the main member comprises a through-hole which is formed through the main member, and the apparatus further comprising a closing member which closes an upper opening of the through-hole, the cylinder bore including an upper portion of the through-hole that is defined by, and between, the closing member and an upper end surface of the hollow sleeve.
(14) According to a fourteenth feature of the present invention that includes any one of the first to thirteenth features (1) to (13), the EC transferring apparatus further comprises at least one detectable portion which is substantially integral with the shaft member, and a detector which is supported by the movable member and which detects the detectable portion, the detectable portion and the detector cooperating with each other to provide a stroke-end detector which detects at least one of an upper stroke end and a lower stroke end of the movement of the shaft member relative to the movable member. In response to detection of at least one of the upper stoke end and the lower stroke end of the movement of the shaft member, the component holder may release the EC, or the movable member may start moving. Thus, the component holder is prevented from releasing the EC before the shaft member reaches its lower stroke end, and the movable member is prevented from starting moving before the shaft member reaches its upper stroke end. That is, the component holder is assuredly prevented from interfering with other members.
(15) According to a fifteenth feature of the present invention that includes any one of the first to fourteenth features (1) to (14), the movable member has at least one pressurized-air supply-and-relief passage which is communicated with the air-pressure-operated cylinder device.
(16) According to a sixteenth feature of the present invention that includes any one of the first to fifteenth features (1) to (15), the shaft member and the movable member have respective vacuum-supply passages which are kept communicated with each other while the shaft member is rotated, and is moved in the axial direction thereof, relative to the movable member, and the vacuum-supply hole of the suction nozzle is connected to the respective vacuum-supply passages of the shaft member and the movable member. When the shaft member is rotated, the phase thereof relative to the movable member changes; and when the shaft member is moved in its axial direction, the position thereof relative to the movable member also changes. However, the vacuum-supply hole of the suction nozzle is kept supplied with vacuum or negative air pressure. Thus, the EC is prevented from falling off the suction nozzle.
(17) According to a seventeenth feature of the present invention that includes any one of the first to sixteenth features (1) to (16), the EC transferring apparatus comprises a plurality of the shaft members, the movable member having a plurality of the support holes which support the plurality of shaft members, respectively, on a circle whose center is positioned on an axis line of the drive wheel about which the drive wheel is rotatable; and a plurality of the driven wheels each of which is substantially integral with a corresponding one of the plurality of shaft members, the drive wheel being meshed with the plurality of the driven wheels to simultaneously rotate the driven wheels. Since each of the shaft members is provided in series with an air cylinder in the axial direction of the each shaft member, a dimension of the each shaft member and the air cylinder in their radial direction is small. In addition, the drive wheel and a rotating device for rotating the drive wheel can be used commonly for the plurality of shaft members. Thus, a dimension of the present apparatus as a whole in a direction perpendicular to the axial direction of the shaft members can be reduced. Therefore, the present EC transferring apparatus enjoys a low production cost and a compact construction.
(18) According to an eighteenth feature of the present invention, there is provided an electric-component mounting system comprising an electric-component mounting apparatus comprising an electric-component transferring apparatus according to any one of the first to seventeenth features (1) to (17); an electric-component supplying device which supplies electric components to the electric-component mounting apparatus; and a board supporting device which supports a printed circuit board on which the electric components are mounted by the electric-component mounting apparatus.
(19) According to a nineteenth feature of the present invention that includes the eighteenth feature (18), the moving device of the electric-component transferring apparatus moves the movable member in each of a first direction parallel to an X axis and a second direction parallel to a Y axis, the X and Y axes being perpendicular to each other on a substantially horizontal plane.
(20) According to a twentieth feature of the present invention that includes the nineteenth feature (19), the board supporting device comprises a printed-circuit-board conveying device which conveys the printed circuit board along a straight reference line and stops the board at a position corresponding to the electric-component transferring apparatus.
(21) According to a twenty-first feature of the present invention that includes the twentieth feature (20), the electric-component mounting apparatus comprises a plurality of component mounting units which are arranged along a straight line parallel to the reference line and each of which has a component-mount region in which the each component mounting unit is allowed to mount electric components on the printed circuit board, and the printed-circuit-board conveying device conveys, along the reference line, the printed circuit board at a predetermined convey pitch which is not longer than a length of the component-mount region of the each component mounting unit.
(22) According to a twenty-second feature of the present invention that includes the twenty-first feature (21), the electric-component supplying device comprises a plurality of unit groups each of which comprises a plurality of component supplying units, each of the plurality of component supplying units storing electric components of a corresponding one of a plurality of sorts, and including a component-supply portion from which the each component supplying unit supplies the electric components one by one, the plurality of component supplying units of the each unit group being arranged along a straight line parallel to the reference line, the plurality of component mounting units corresponding to the plurality of unit groups, respectively.
(23) According to a twenty-third feature of the present invention that includes any one of the eighteenth to twenty-second features (18) to (22), the electric-component transferring apparatus comprises at least one pair of the component holders each of which sucks and holds an electric component supplied from the electric-component supplying device, by applying vacuum to the electric component; the movable member supporting the one pair of component holders; an image taking device which has a square range of view and which takes respective images of the electric components held by the one pair of component holders; an error detecting and correcting device which is connected to the image taking device and which detects and corrects, based on the taken image of each of the electric components held by the one pair of component holders, at least one of (a) a positional error of the each electric component from a reference position in at least one direction parallel to a plane on which the printed circuit board is supported by the board supporting device and (b) an angular error of the each electric component from a reference angular position about an axis line perpendicular to the plane, so that the electric components are mounted on the printed circuit board after the at least one of the positional error and the angular error of the each electric component is corrected; the moving device moving the movable member from a component-receive position where each of the component holders of the one pair is opposed to the electric-component supplying device, to a component-mount position where the each component holder mounts the electric component on the printed circuit board supported by the board supporting device, via an image-take position where the movable member is stopped by the moving device such that respective axis lines of the component holders of the one pair perpendicularly intersect one of two diagonal lines of the square range of view of the image taking device, at respective positions which are axis-symmetric with each other with respect to an optical axis of the image taking device, so that the image taking device simultaneously takes the respective images of the electric components held by the one pair of component holders.
(24) According to a twenty-fourth feature of the present invention, there is provided a method of taking respective images of a plurality of electric components, comprising the steps of positioning a pair of component holders each of which sucks and holds an electric component by applying vacuum thereto, relative to an image taking device having a square range of view, such that respective axis lines of the two component holders of the pair perpendicularly intersect one of two diagonal lines of the square range of view of the image taking device, at respective positions which are axis-symmetric with each other with respect to an optical axis of the image taking device, and operating the image taking device to simultaneously take respective images of the electric components held by the pair of component holders. The two ECs held by the two component holders falls within the range of view of the image taking device, and the respective images of the two ECs are simultaneously taken by the image taking device. Therefore, the present method improves the efficiency of taking EC images, as compared with a method in which an image taking device takes an image of only a single EC at one time. The optical axis of the image taking device coincides with the center of the range of view thereof. Since the two component holders are aligned with one of the two diagonal lines of the range of view, at the respective positions axis-symmetric with each other with respect to the optical axis, the two holders can be prevented from interfering with each other. In addition, since the two component holders can be positioned within the limited or narrow range of view of the image taking device, the narrow range of view can be efficiently utilized. Moreover, the present method can be used for simultaneously taking respective images of a pair of ECs of any sort in a wide range of dimensions or sizes. Thus, the present method largely improves the EC-image taking efficiency by simultaneously taking respective images of two ECs.
(25) According to a twenty-fifth feature of the present invention that includes the twenty-fourth feature (24), the step of positioning the pair of component holders comprises moving a single movable member which supports a plurality of pairs of the component holders, and sequentially positioning each pair of component holders of the plurality of pairs of component holders, relative to the image taking device, such that respective axis lines of the component holders of the each pair perpendicularly intersect a corresponding one of the two diagonal lines of the square range of view of the image taking device, at respective positions which are axis-symmetric with each other with respect to the optical axis of the image taking device, and the step of operating the image taking device comprises operating the image taking device to simultaneously take respective images of the electric components held by the each pair of component holders. After respective images of two ECs held by one pair of component holders are taken by the image taking device, the movable member is moved and stopped so that respective images of two ECs held by another, or the other, pair of component holders are taken. Even through the movable member may support a great number of pairs of component holders, the present method reduces, to half, the time needed for taking respective images of all ECs, as compared with the method in which an image of only a single EC is taken at one time. Thus, the present method improves the EC-image taking efficiency. In the case where the movable member supports the plurality of pairs of component holders such that a straight line which perpendicularly intersects the respective axis lines of the two component holders of each pair is parallel to a corresponding one of the two diagonal lines of the range of view, the two component holders of the each pair can be easily positioned relative to the range of view. However, it is not essentially required that the movable member support the plurality of pairs of component holders such that all the straight lines for the plurality of pairs of component holders are parallel to the corresponding diagonal lines of the range of view. For example, in the case where the movable member is provided by a rotatable member, the movable member may support the plurality of pairs of component holders such that one or more of the straight lines for the plurality of pairs of component holders are not parallel to the corresponding diagonal lines of the range of view. In this case, however, the straight line which perpendicularly intersects the respective axis lines of the two component holders of each pair can be made parallel to the corresponding one of the two diagonal lines, by rotating the rotatable member. That is, the rotatable member can be stopped at a position where the respective axis lines of the component holders of each pair perpendicularly intersect the corresponding one of the two diagonal lines of the square range of view of the image taking device, at the respective positions axis-symmetric with each other with respect to the optical axis of the image taking device.
(26) According to a twenty-sixth feature of the present invention, there is provided an electric-component mounting system comprising a circuit-substrate supporting device which supports a circuit substrate; an electric-component supplying device which supplies electric components; at least one pair of component holders each of which sucks and holds an electric component supplied from the electric-component supplying device, by applying vacuum to the electric component; a movable member which supports the one pair of component holders; an image taking device which has a square range of view and which takes respective images of the electric components held by the one pair of component holders; an error detecting and correcting device which is connected to the image taking device and which detects and corrects, based on the taken image of each of the electric components held by the one pair of component holders, at least one of (a) a positional error of the each electric component from a reference position in at least one direction parallel to a plane on which the circuit substrate is supported by the circuit-substrate supporting device and (b) an angular error of the each electric component from a reference angular position about an axis line perpendicular to the plane, so that the electric components are mounted on the circuit substrate after the at least one of the positional error and the angular error of the each electric component is corrected; a moving device which moves the movable member from a component-receive position where each of the component holders of the one pair is opposed to the electric-component supplying device, to a component-mount position where the each component holder mounts the electric component on the circuit substrate supported by the circuit-substrate supporting device, via an image-take position where the moving device stops the movable member such that respective axis lines of the component holders of the one pair perpendicularly intersect one of two diagonal lines of the square range of view of the image taking device, at respective positions which are axis-symmetric with each other with respect to an optical axis of the image taking device, so that the image taking device simultaneously takes the respective images of the electric components held by the one pair of component holders. The movable member may be a linearly movable member which is linearly movable in at least one of an X-axis direction and a Y-axis direction which are perpendicular to each other on a plane perpendicularly intersecting the respective axis lines of the two component holders. Otherwise, the movable member may be one or ones which supports or support the pair of component holders such that the component holders are revolved about a common axis line. In the latter case, the present EC mounting system may include a component-holder positioning device which sequentially positions the component holders at at least one predetermined operation position on the locus of revolution of the holders. The component-holder positioning device may be one which is disclosed in Japanese Patent Application laid open for public inspection under Publication No. 9-237,997 corresponding to U.S. patent application Ser. No. 08/769,700 assigned to the assignee of the present application. The disclosed positioning device includes, as the movable member, a plurality of rotary members which are rotatable about a common axis line, independent of each other, and additionally includes a rotary-motion applying device as a movable-member moving device which applies, to each of the rotary members, such a rotary motion which causes the each rotary member to be fully rotated by 360 degrees about the common axis line, be stopped at least three times during the full rotation, and keep a predetermined time difference from each of its preceding and following rotary members. The plurality of rotary members support the plurality of component holders, respectively, at respective positions equally distant from the common axis line. The rotary-motion applying device may be adapted to stop simultaneously two rotary members at an image-take position as one of the operation positions where respective images of the two ECs held by the two holders supported by the two rotary members are simultaneously taken by the image taking device. Otherwise, each of the plurality of rotary members may support a pair of component holders, and the rotary members may be sequentially stopped at the image-take position where respective images of the two ECs held by the two component holders supported by the each rotary member are simultaneously taken. Otherwise, the component-holder positioning device may be one which is disclosed in Japanese Patent No. 2,644,914. This positioning device includes, as the movable member, an intermittent-rotation body which is intermittently rotatable about an axis line, and additionally includes a rotation-body rotating device as a movable-member moving device that intermittently rotates the rotation body. The rotation body supports the plurality of component holders such that the component holders are equiangularly spaced from each other at a predetermined angular-spacing pitch equal to a predetermined intermittent-rotation pitch at which the rotation body is intermittently rotated by the rotating device. In addition, the rotation body supports the plurality of component holders such that respective axis lines of each pair of adjacent component holders perpendicularly intersect one of the two diagonal lines of the square range of view of the image taking device, at the respective positions axis-symmetric with each other with respect to the optical axis of the image taking device. The intermittent-rotation body may be one which is rotatable in each of opposite directions. The intermittent-rotation body may be replaced with a rotatable body which is rotatable by an arbitrary angle in each of opposite directions. U.S. patent application Ser. No. 08/977,662 assigned to the assignee of the present application discloses a positioning-device moving device which moves the above-described component-holder positioning device as a whole to an arbitrary position on an EC-convey plane which bridges the circuit-substrate (xe2x80x9cCSxe2x80x9d) supporting device and the EC supplying device. In the latter case, the positioning-device moving device cooperates with the rotary-motion applying device and the rotation-body rotating device to provide the movable-member moving device. The present EC mounting system performs the same number of EC-image taking operations as the number of xe2x80x9cpairsxe2x80x9d of the component holders. Therefore, the present system reduces, to half, the time needed for taking respective images of all ECs, as compared with a method in which an image of only one EC is taken at one time. Thus, the present system can mount ECs on CSs with high efficiency. The positional error of the EC held by each component holder from the reference position may be corrected by correcting the distance of movement of the movable member, or correcting the position where the CS is positioned by the CS supporting device. The angular error of the EC held by each component holder from the reference angular position is an angular- or rotation-position error of the EC about its own axis line. In the case where the movable member supports the component holders such that each of the component holders is rotatable relative to the movable member, according to the twenty-seventh feature (27) described below, the angular error of the EC held by the each component holder may be corrected by operating a holder rotating device to rotate the each holder about its axis line. In the last case, the holder rotating device may be provided on the movable member, or otherwise may be provided, separately from the movable member, at a holder-rotate position fixed on a route along which the movable member is moved by the movable-member moving device.
(27) According to a twenty-seventh feature of the present invention that includes the twenty-sixth feature (26), the EC mounting system comprises a plurality of pairs of the component holders which are supported by the movable member such that each of the component holders is rotatable relative to the movable member. In the present system, the angular error of the EC held by each component holder may be corrected by rotating the each component holder. More specifically, based on a batch of image data representative of the image of the EC taken by the image taking device, the error detecting and correcting device calculates the positional error and the angular error of the EC. This angular error is corrected by rotating the each holder holding the EC. In the case where the plurality of component holders are rotated by a common drive wheel and a common rotating device, according to the twenty-eighth feature (28) described below, the component holders are provided on a single circle whose center is positioned on the axis line of rotation of the drive wheel. However, so long as each of the component holders can be rotated, it is not essentially required that the component holders be provided on a single circle, that is, it is possible that the component holders be provided at respective arbitrary positions.
(28) According to a twenty-eighth feature of the present invention that includes the twenty-seventh feature (27), the EC mounting system further comprises a drive wheel which is supported by the movable member such that the drive wheel is rotatable about an axis line; a rotating device which is supported by the movable member and which rotates the drive wheel about the axis line; the plurality of pairs of component holders being supported by the movable member such that respective axis lines of the component holders about which the component holders are rotatable, respectively, perpendicularly intersect a circle whose center is located on the axis line of rotation of the drive wheel; and a plurality of driven wheels each of which is substantially integral with a corresponding one of the component holders, the drive wheel being meshed with the driven wheels to simultaneously rotate the driven wheels. When the drive wheel is rotated, the driven wheels meshed with the drive wheel are simultaneously rotated so that all the component holders are simultaneously rotated about their own axis lines, respectively. The angular error of the EC held by each of the component holders may be corrected by rotating the each holder about its own axis line. After the current EC is mounted on the CS, the next EC following the current EC is rotated to correct its angular error. However, when the next holder holding the next EC is rotated by a certain angle, the other holders are also rotated by the same angle. Therefore, the current angular position of each of the second and following ECs includes a correcting angle or angles used to rotate the preceding EC or ECs to correct its or their angular error or errors. Thus, the angular error of each of the second and following ECs is corrected by rotating the drive wheel by a correcting angle and in a correcting direction. The correcting angle and direction are determined by taking into account the correcting angle or angles for its preceding EC or ECs. The correcting direction may be selected as one of opposite directions in such a manner that the drive wheel is rotated in the selected one direction, by the correcting angle which is smaller than an angle by which the drive wheel is rotated in the other direction. Since the drive wheel and the rotating device are supported by the movable member, the angular error of the EC held by each of the component holders may be corrected while the movable member is moved. In addition, since the drive wheel and the rotating device are commonly to the plurality of component holders, the present EC mounting system enjoys a low manufacturing cost.
(29) According to a twenty-ninth feature of the present invention that includes the twenty-eighth feature (28), the axis line of rotation of the drive wheel is parallel to the respective axis lines of rotation of the component holders. The above-identified U.S. patent application Ser. No. 08/977,662 discloses, as the movable member, a rotatable body which is rotatable about an axis line and which supports the plurality of pairs of component holders such that each pair of holders extend along a corresponding one of a plurality of generating lines of a conical surface whose center line coincides with the axis line of rotation of the rotatable body. In this case, the axis line of rotation of the rotatable body is inclined relative to a vertical line by an angle at which one of the generating lines of the conical surface perpendicularly intersects a horizontal plane along which a CS supporting device and an EC supplying device provided. The respective axis lines of rotation of the component holders are inclined relative to the axis line of rotation of the drive wheel that is parallel to the axis line of rotation of the rotatable body. Each of the component holders holds and mounts an EC at a position where the axis line of the each component holder is parallel to the vertical line. The image taking device takes EC images at a position where the axis line of the each component holder is inclined relative to the vertical line or the horizontal plane, and the range of view of the image taking device is inclined relative to the horizontal plane. In this case, when the image taking device simultaneously takes respective images of two ECs held by each pair of adjacent component holders at the image-take position, the respective postures or attitudes of the two ECs are inclined by a small angle, because of their own weights, relative to a plane perpendicular to the optical axis of the image taking device. In contrast, in the present EC mounting system, the axis line of rotation of the drive wheel is parallel to the respective axis lines of rotation of the component holders. Therefore, the present system is free from the above-indicated problem.
(30) According to a thirtieth feature of the present invention that includes any one of the twenty-seventh to twenty-ninth features (27) to (29), the plurality of pairs of component holders are located on a circle whose center is located on the axis line of rotation of the drive wheel, such that one pair of component holders are spaced from another pair of component holders by 90 degrees about the axis line of rotation of the drive wheel. The movable member may support two, three, or four pairs of component holders, i.e., four, six, or eight component holders in total. It is not essentially required that one pair of component holders be spaced from another, or the other, pair of component holders by 90 degrees about the axis line of rotation of the drive wheel. However, in the case where two or more pairs of holders are spaced from each other by 90 degrees, a straight line which perpendicularly intersects the respective axis line of one pair of holders is parallel, or perpendicular, to a straight line which perpendicularly intersects the respective axis line of another, or the other, pair of holders. Therefore, each of the two or more pairs of holders can be positioned on a corresponding one of the two diagonal lines of the range of view, by just translating the movable member without having to rotating the same.
(31) According to a thirty-first feature of the present invention that includes any one of the twenty-sixth to thirtieth features (26) to (30), the moving device moves the movable member in each of an X-axis direction parallel to an X axis and a Y-axis direction parallel to a Y axis, the X axis and the Y axis being perpendicular to each other on a plane parallel to a support plane on which the circuit substrate is supported by the circuit-substrate supporting device.